The present invention generally relates to luminaires, and more particularly to luminaires employing baffles or louvers in their down light openings to shield the luminaire's light source from direct view. The invention has particular application in connection with suspended linear fluorescent lighting having baffled down light openings, but can also be applied to other types of suspended or recessed lighting where baffles or louvers are used. As used herein, the terms "baffles" and "louvers" may be used interchangeably.
Luminaires are used for overhead lighting in a wide variety of commercial, institutional, and office environments. Such luminaires are usually characterized as direct luminaires, indirect luminaires or direct/indirect luminaires, depending on how the source light is delivered from the luminaire to the space below. In the case of a totally indirect luminaire, the luminaire's light source is hidden within the luminaire housing, and thus the surfaces of the lamps which act as the source of light are shielded from view. However, in the case of luminaires that produce direct lighting, the lamps of the luminaire are typically exposed through a down light opening in the bottom of the luminaire, which must be shielded to avoid visual discomfort associated with exposed lamp surfaces. One form of shielding is to use a plastic lens or diffuser plate which covers the down light opening. The difficulty with such shielding is that it traps heat and causes the luminaire to operate less efficiently. Also, the visible surfaces of the lens or diffuser plates are themselves relatively bright, thereby creating their own source of visual discomfort.
To overcome the problems associated with lenses and diffusers, lighting designers frequently specify direct (or direct-indirect) luminaires having open baffle structures which shield the luminaire lamps at angles where the introduction of glare is of greatest concern, yet which allow the lamps to burn at a cooler temperature and thus more efficiently. Conventional baffle structures usually include a series of parallel baffle elements or a grid pattern of baffles (usually referred to as a louver) arranged in the luminaire's down light opening to shield the lamps at normal viewing angles at any distant position around the luminaire. For efficiency, the baffle surfaces are typically reflectors and thus can themselves become a source of unwanted excessive brightness. To prevent this, so-called "parabolic" baffles are now most commonly used, instead of straight baffles. Parabolic baffles have curved specular reflective surfaces that control reflections in a manner that essentially eliminates any substantial surface brightness within shielded viewing angles. Importantly, by using parabolic baffles, a lighting designer can readily control brightness to meet limitations established by the ANSI RP-1 standards adopted in 1993 for direct lighting in the video display terminal (VDT) environments commonly found in present day offices. In such lighting environments, RP-1 compliant luminaires are critical to avoiding the undesirable effects of direct and reflected glare on the comfort of a worker who spends substantial time in front of a VDT screen.
However, the recognized advantages of parabolic baffles have given rise to what many consider to be a distinct drawback for luminaires which use such baffles: at normal viewing angles, and in particular angles controlled by the RP-1 standard, the baffled down light opening of the luminaire normally appears dark without any substantial clue as to the source of the down light. This can be a particular disadvantage in many lighting environments, such as open offices, where task-based recommended lighting levels are relatively low, down to about 30 footcandles. In such environments visual comfort and overall lighting quality actually suffer from the absence of visual clues as to the source of light, since in absence of such visual clues the illuminated space will often appear to be too dark and/or devoid of visual interest. In addition, the very presence of a dark void in the luminaire's down light opening resulting from a well-designed parabolic baffle structure is considered by many to be psychologically unpleasant, due to a lack of perceptible brightness.
The present invention overcomes the above-mentioned disadvantages of parabolic down light baffle structures while preserving the benefits of an open shielding structure, that is, the ability to gain efficiency while shielding the light source at desired viewing angles without introducing excessive brightness. The invention, which can be used in many different lighting environments in addition to the VDT environment, provides effective shielding while providing visual interest along with visual clues as to the location of the light source. The baffle structures of the invention will generally improve the quality of direct lighting received from shielded overhead lighting fixtures, and will eliminate the "dark hole" effect associated with parabolic baffles and louvers. The invention can also be used to introduce specific orientation and circulation information in any space whether architectural or in an outdoor setting.